Our group has developed a model for lipid transport between blood and tissue by lateral movement in a continuum of cell membranes. Last year we reported findings in adipose tissue and heart of suckling rats that gave morphological evidence for the model. Our studies have now been extended to include brown fat of suckling rats, and heart, liver and white adipose tissue of adult rats. We present herein evidence that the membrane of endoplasmic reticulum is continuous with plasma membrane in liver and adipose tissue of adult rats, and that the membrane of sarcoplasmic reticulum in adult rats heart is continuous with the outer mitochondrial membrane as well as with plasma membrane. Thus, our new findings indicate that the interfacial continuum of membranes proposed for fatty acid transport from capillaries to endoplasmic reticulum in parenchymal cells can be extended to include delivery of fatty acids to mitochondria for oxidation. Phase microscopic study of ionizing oleic acid shows that ionized oleic acid immeditely entered the lipid-water interface and that growth of the interface formed filaments and finger-like structures. Also, very little if any of the fatty acids desorbed as monomers into the aqueous phase at pH less than 9.